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Preparation of Polycaprolactone Nanoparticles Via Supercritical Carbon Dioxide Extraction of Emulsions

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Preparation of Polycaprolactone Nanoparticles Via Supercritical Carbon Dioxide Extraction of Emulsions Drug Deliv. and Transl. Res. DOI 10.1007/s13346-017-0422-3 ORIGINAL ARTICLE Preparation of polycaprolactone nanoparticles via supercritical carbon dioxide extraction of emulsions Adejumoke Lara Ajiboye1 & Vivek Trivedi1 & John C. Mitchell1 # The Author(s) 2017. This article is an open access publication Abstract Polycaprolactone (PCL) nanoparticles were pro- rapidly increased over the years because they can successfully duced via supercritical fluid extraction of emulsions (SFEE) maximise the efficacy of the drug molecules [1]. using supercritical carbon dioxide (scCO2).Theefficiencyof Nanoparticles are particles with a diameter range from 1 to the scCO2 extraction was investigated and compared to that of 100 nm, even though the dynamic range can cover the whole solvent extraction at atmospheric pressure. The effects of pro- nanometre scale [2]. As a drug delivery system, nanoparticles cess parameters including polymer concentration (0.6–10% can entrap drugs or biomolecules into their internal structures w/w in acetone), surfactant concentration (0.07 and 0.14% and/or adsorb these drugs or biomolecules onto their external w/w) and polymer-to-surfactant weight ratio (1:1–16:1 w/w) surfaces [3]. on the particle size and surface morphology were also inves- Due to their particle size, nanoparticles can move freely tigated. Spherical PCL nanoparticles with mean particle sizes through the body via the smallest capillary vessels, cell and between 190 and 350 nm were obtained depending on the tissue gaps in order to reach their target organs [4]. These polymer concentration, which was the most important factor properties of nanoparticles help to modify the bio- where increase in the particle size was directly related to total distribution and pharmacokinetic properties of the adsorbed/ polymer content in the formulation. Nanoparticles produced entrapped drug molecules leading to an improvement in the were analysed using dynamic light scattering and scanning efficacy of the drug, decrease in unwanted side-effects and electron microscopy. The results indicated that SFEE can be increase in patient compliance [5]. Nanoparticles can be pre- applied for the preparation of PCL nanoparticles without ag- pared from inorganic or polymeric materials. Polymeric nano- glomeration and in a comparatively short duration of only 1 h. particles are more common and appropriate as they can be chemically modified to be biodegradable and biocompatible Keywords Solvent extraction . Polycaprolactone . [6]. Biodegradable substances are broken down in vivo either Nanoparticles . Supercritical carbon dioxide . Supercritical enzymatically or non-enzymatically or both, to give rise to fluid extraction of emulsions toxicologically safe by-products which are further removed by the normal metabolic pathways. The use of biodegradable polymers has greatly increased over the past decade, and they Introduction can generally be classified as either (1) synthetic biodegrad- able polymers which include relatively hydrophobic materials for example poly-lactic-co-glycolic acid (PLGA), The use of drug delivery systems, particularly the micro- and polycaprolactone (PCL) and others, or (2) naturally occurring nano-scale intelligent systems for therapeutic molecules has polymers such as chitosan, hyaluronan, etc. [7]. Principally, synthetic polymers have many inherent advantages since their * Vivek Trivedi structures can be manipulated to generate specialised carriers [email protected] to suit particular applications [8]. PCL is a semi-crystalline polyester that is hydrophobic, 1 Faculty of Engineering and Science, University of Greenwich, biodegradable and biocompatible. When compared to other Central Avenue, Chatham Maritime, Kent ME4 4TB, UK polymers, the biodegradation of PCL is slow; hence, it can Drug Deliv. and Transl. Res. be highly suitable for the design of controlled release delivery SFEE have an ordered size and morphology because emulsifi- systems [9–11]. The glass transition temperature (Tg)of cation process provides a template and the fast kinetics of the − 60 °C and low melting point (59–64 °C) of PCL allows scCO2 extraction prevents particle agglomeration [22]. for the easy fabrication of delivery systems at reasonably The aim of this work was to produce polymeric nanoparticles low temperatures [10]. Furthermore, PCL has an excellent by employing scCO2 extraction of the solvent in the organic blend compatibility with other polymers which facilitates tai- phase of nano-emulsions prepared via spontaneous emulsifica- loring of desired properties like degradation kinetics, hydro- tion. The major objective of this work was to study the suitability philicity and mucoadhesion [12, 13]. of SFEE and the effect of various parameters influencing the In the last decades, PCL polymers have been a key area of preparation of nanoparticles using PCL as a model polymer. interest in the development of controlled delivery systems espe- The effect of parameters including polymer and surfactant con- cially for peptides and proteins [14]. These systems using PCL centration on the particles’ hydrodynamic diameter, polydisper- or PCL blends have shown to be useful in varied conditions. For sity index (PDI) and zeta potential was investigated. The time example, while developing PCL microspheres for vaccine de- and the optimum CO2 flow rate were also determined for the livery, Jameela et al. showed that PCL has good permeability to complete extraction of oil phase/solvent at both high pressures in proteins and contrary to poly (lactic acid) PLA and poly glycolic scCO2 and atmospheric conditions. acid (PGA), PCL degrades very slowly and does not give rise to an acidic environment which can negatively affect the antigenic- ity of the vaccine, and thus, it can be used as a vaccine carrier Experimental section [15]. Observations by Youan et al. also suggested that PCL delivery systems are unaffected by simulated gastric fluid and Materials hence could give some protection to the encapsulated peptide from proteolytic destruction in the stomach, allowing the PCL (Mw = 45,000 Da) was obtained from Shenzhen ESUN, entrapped drugs to pass unharmed into the intestine for presen- China, and Tween 80 and acetone were purchased from Sigma tation to the gut-associated lymphoid system [16]. Aldrich, UK. Liquid CO2 at 99.9% was supplied by BOC Ltd., Various techniques can be employed to prepare nanoparticles, UK. All chemicals were of analytical grade and used without many of which involve a type of emulsion evaporation. The any further purification. Deionised water was used throughout preparation of nano-emulsions via spontaneous emulsification the study. mechanism using a water-miscible solvent is an established method that allows for the generation of nano-sized droplets Methods [17]. Nano-emulsions are made of fine oil-in-water dispersions with droplet sizes ranging from 100 to 600 nm. They can be Oil-in-water emulsion preparation prepared using a small surfactant concentration and they typical- ly exhibit low oil-water interfacial tensions. Spontaneous emul- The nano-emulsions were prepared through spontaneous emul- sification occurring when the organic and aqueous phases are in sification mechanism. The method used for the preparation of contact determines the droplet size and size distribution, and PCL emulsions was adapted from the work reported by Prieto depends on variables including bulk viscosity, surfactant con- and Calvo [22]. The organic phase consists of a homogenous centration and structure [17–19]. In this work, the organic phase solution of PCL in acetone and Tween 80, while deionised water consists of a homogenous solution of the polymer in a water- made up the aqueous phase. In summary, an appropriate quantity miscible solvent (acetone) and surfactant which is mixed with of PCL was first dissolved in acetone (0.6–10% w/w)inather- the aqueous phase to produce nano-emulsion. mostatic water bath at 40 °C, before the addition of surfactant in Although emulsification of polymer mixtures is known to be a centrifuge tube to obtain required concentrations (0.07 and an efficient method, it can be associated with limitations 0.14%) or ratios (1:1–16:1 w/w). The contents in the tube were concerning process efficiency and control of the particle size mixed together using a vortex mixer for 1 min. After vortexing, and distribution when particles are being recovered from the 35.8 g of warm deionised water (40 °C) was added, and the tube emulsion through conventional processes [20]. Supercritical flu- was placed back on the vortex mixer for 5 min in order to form a id extraction of emulsion (SFEE) is a novel particle formation homogenous emulsion. Solvent extraction was carried out im- technique where it employs a supercritical fluid (SCF) such as mediately after emulsion was prepared. supercritical carbon dioxide (scCO2) to rapidly extract the sol- vent or oil phase of an emulsion. The removal of the solvent Solvent extraction via SFEE leads to the precipitation of the solute resulting into an aqueous suspension containing nanoparticles. Particles can thereafter be SFEE was conducted in a batch mode where 25-g emulsion was recovered from the aqueous suspension by centrifugation and/or introduced in the high-pressure vessel (Thar Process Inc., USA) by evaporation at room temperature [21]. Particles generated via pre-heated to 40 °C (± 2 °C), the vessel was then closed and Drug Deliv. and Transl. Res. liquid CO2 was pumped until a pressure of 100 bar was Results and discussion achieved.
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